The present invention relates to vibration control systems, and more particularly to vibration absorbers for reducing structural vibrations.
Vibration absorbers generally include a mass coupled with a spring and are used to control vibrations that occur within the member to which they are attached. They are typically resonant devices and their natural frequencies are generally tuned to coincide with a predominant disturbance frequency of the vibrating member. Examples of vibration absorbers may be found in U.S. Pat. Nos. 3,288,419; 3,322,379; 3,388,772; 3,490,556; 3,668,939; 3,767,181; 4,230,291; 4,697,781; 4,852,848; 5,052,530 and 5,072,801.
One known beneficial application of vibration absorbers is on above-ground pipelines. Pipelines are often used to transfer fluids, such as oil and natural gas, across large distances. In many instances, these pipelines are installed above-ground by suspending the pipeline on spaced-apart supports. Pipelines, however, may be susceptible to damage from vibrations that may occur due to such things as wind-induced vortex shedding and earthquakes. An example of an application of a vibration absorber to a pipeline is described in U.S. Pat. No. 5,193,644 to Hart et al. Hart et al. describes a vibration damper that includes a mass suspended from a pipeline by interconnected damper members which generally act as a linear spring. Other examples of a vibration absorbers used in conjunction with a pipe are found in U.S. Pat. Nos. 4,576,356 and 4,716,986.
According to the present invention, vibration absorbers are provided which utilize a torsional spring and a dynamic mass to control vibrations that occur within a structure to which they are attached. Additionally, pipeline systems are provided which utilize such vibration absorbers to control vibrations that occur within the pipeline system. In various embodiments of the present invention, the torsional spring is one or more elastomer elements connected between the dynamic mass and a support frame to produce a spring force responsive to pivotal rotation of the dynamic mass relative to the support frame. In various embodiments, one or more elastomer elements arranged in series or in parallel may be used as the torsional spring to provide a desired vibratory dampening characteristic for applications, such as pipelines. Use of such torsional springs may provide a more simplified design with less mechanical joints which may be less susceptible to failure in harsh environments.
In embodiments of the present invention, the vibration absorber includes a support frame, a dynamic mass pivotally connected to the support frame for movement about a pivotal axis and a torsional spring connected between the dynamic mass and the support frame that provides a spring force responsive to pivotal rotation of the dynamic mass relative to the support frame. The torsional spring may be positioned along the pivotal axis. The torsional spring may be a coil spring or an elastomer element. The elastomer element may include a elastomeric disc. The elastomeric disc may be made from a material selected from the group consisting of natural rubber elastomer, synthetic elastomer or a blend of natural rubber elastomer and synthetic elastomer.
In other embodiments of the present invention, the support frame includes a first side member and a second side member offset from the first side member along the pivotal axis. The dynamic mass may be positioned between the first side member and the second side member along the pivotal axis.
In further embodiments of the present invention, the elastomer element further includes a first plate. The first plate may be connected to the elastomeric disc between the elastomeric disc and the first side member along the pivotal axis. The first plate may be connected to the first side member at a radial position offset from the pivotal axis. The first side member may include a slot configured to provide selectable rotational orientation of the dynamic mass relative to the support frame.
In still further embodiments of the present invention, the dynamic mass includes an arm and an adjustment mass movably mounted on the arm. The adjustment mass may include a plurality of metal plates. The arm may include a channel having a track formed therein such that the adjustment mass may be moved along the track to adjust a dynamic characteristic of the vibration absorber. The elastomer element may be connected between the first side member and the arm. The elastomer element may include a second plate that may be connected to the elastomeric disc. The second plate may also be connected to the side of the arm.
In still further embodiments of the present invention, the torsional spring further includes a second elastomer element connected between the second side member and the arm. The second elastomer element may, alternatively, be connected between the first elastomer element and the arm.
In still other embodiments of the present invention, the vibration absorber includes a support frame including a first side member and a second side member offset from the first side member, a dynamic mass pivotally connected to the support frame for movement about a pivotal axis, and an elastomer element connected between the dynamic mass and the support frame that provides a spring force responsive to pivotal rotation of the dynamic mass relative to the support frame. The elastomer element and the dynamic mass may be positioned between the first side member and the second side member along the pivotal axis. The vibration absorber may include a plurality of elastomer elements positioned between the first side member and the second side member along the pivotal axis. The elastomer elements may all be connected between the first side member and the arm. Alternatively, at least one elastomer element may be connected between the first side member and the arm and at least one elastomer element may be connected between the second side member and the arm.
In still further embodiments of the present invention, the vibration-reduced pipeline system includes a pipeline section and a vibration absorber connected to the pipeline section. The vibration absorber may include a support frame connected to the pipeline section, a dynamic mass pivotally connected to the support frame for movement about a pivotal axis, and a torsional spring connected between the dynamic mass and the support frame that provides a spring force responsive to pivotal rotation of the dynamic mass relative to the support frame.